docs: def _tab(max_i=None):
      """Extraction and caching of IAU1980 nutation coefficients
      """
  
      filepath = Path(__file__).parent / "data" / "tab5.1.txt"
  
      result = []
      with filepath.open() as fhd:
          i = 0
          for line in fhd.read().splitlines():
              if line.startswith("#") or not line.strip():
                  continue
  
              fields = line.split()
              result.append(([int(x) for x in fields[:5]], [float(x) for x in fields[6:]]))
  
              i += 1
              if max_i and i >= max_i:
                  break
  
      return result